AB0866 SEASONAL VARIATION OF SERUM KL-6 LEVELS IN PATIENTS WITH SYSTEMIC SCLEROSIS-ASSOCIATED WITH INTERSTITIAL LUNG DISEASE
Authors: H. Hirose, T. Higuchi, K. Takagi, A. Tochimoto, Y. Kawaguchi, M. Harigai
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Recent studies have shown that serum KL-6 levels were useful for diagnosing and estimating prognosis in patients with systemic sclerosis-associated with interstitial lung disease (SSc-ILD) <sup>[1-4]</sup>. Additionally, KL-6 has the potential for assessing the activity of SSc-ILD; however, it may fluctuate irrespective of disease activity <sup>[5]</sup>. Identifying the reasons for fluctuation will lead to the utilization of this non-invasive tool. Based on our clinical experience, serum KL-6 levels may have seasonal variations. <h3>Objectives</h3> We aimed to evaluate whether serum KL-6 levels are affected by season in patients with SSc with ILD (SSc-ILD). <h3>Methods</h3> This is a single-center, retrospective observational study. The diagnosis of SSc was according to the 2013 ACR/ EULAR classification criteria, and the presence of ILD was confirmed by computed tomography (CT) or high-resolution CT (HRCT). We defined summer as July to September and winter as December to January. SSc-ILD patients with data of serum KL-6 levels in the 2015 winter (from December 2014 to January 2015), 2015 summer, and 2016 winter were included. Patients with comorbidities that could affect serum KL-6 levels, such as malignancy, pneumocystis pneumonia and alveolar proteinosis, and patients who did not confirm the change in the extent of ILD by chest CT during the observational period were excluded. The extent of ILD was calculated as the average of CT images at the five predefined levels <sup>[6]</sup>, and scoring was blinded. Differences in serum KL-6 levels between summer and winter were analyzed by the Wilcoxon signed-rank test, followed by the Bonferroni correction for adjusting multiple comparisons. <h3>Results</h3> Sixty patients with SSc-ILD were included. 53 (88%) patients were female. At baseline, the median age was 61 (interquartile range [IQR]: 44–66) years, and the median disease duration was 7.7 (IQR: 4.2–13) years. 34 (57%) patients had diffuse cutaneous SSc (Table 1). Regarding the extent of ILD, 18 (30) patients had a lesion area greater than 20%. Eight (15.4%) patients had changed in the extent of ILD, and 52 (84.6%) patients were unchanged. Serum KL-6 levels were significantly higher in the winter than in the summer (2015 summer vs 2015 winter: 585 IU/L vs 648 IU/L, p &lt; 0.0001; 2015 summer vs 2016 winter: 585 IU/L vs 690 IU/L, p &lt; 0.0001). However, there was no difference between the 2015 winter and 2016 winter (p=0.62) (Figure 1). Regarding 52 patients with stable ILD, similar results were obtained (2015 summer vs 2015 winter: 736 IU/L vs 860 IU/L, p &lt; 0.0001; 2015 summer vs 2016 winter: 736 IU/L vs 815 IU/L, p &lt; 0.0001; 2015 winter vs 2016 winter: 815 IU/L vs 860 IU/L, p =0.63). <h3>Conclusion</h3> Serum KL-6 levels may fluctuate regardless of the activity of SSc-ILD. The result of our study may aid the interpretation of serum KL-6 testing. <h3>References</h3> [1]Distler O, <i>et al. Eur Respir J.</i> 2020;55:1902026. [2]Volkmann, <i>et al. Arthritis Rheumatol.</i> 2019;71:2059–2067 [3]Shirai Y, <i>et al. Diagnostics (Basel).</i> 2021; 11:2007. [4]Goh NS, <i>et al. Am J Respir Crit Care Med</i>. 2008;177:1248–1254. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Hikaru Hirose: None declared, Tomoaki Higuchi: None declared, Kae Takagi: None declared, Akiko Tochimoto: None declared, Yasushi Kawaguchi: None declared, Masayoshi Harigai Speakers bureau: AbbVie Japan GK; AstraZeneca K.K.; Ayumi Pharmaceutical Co.; Boehringer Ingelheim Japan Inc.; Bristol Myers Squibb Co., Ltd.; Chugai Pharmaceutical Co., Ltd.; Eisai Co., Ltd.; Eli Lilly Japan K.K.; GlaxoSmithKline K.K.; Gilead Sciences Inc.; Janssen Pharmaceutical K.K.; Kissei Pharmaceutical Co., Ltd.; Nippon Kayaku Co., Ltd.; Nippon Shinyaku Co., Ltd.; Novartis Japan; Pfizer Japan Inc.; CIMIC Holdings Co., Ltd.; Mitsubishi Tanabe Pharma Co.; Teijin Pharma Ltd.; and UCB Japan Co. Ltd., Consultant of: AbbVie; Boehringer-Ingelheim; Bristol Myers Squibb Co.; Kissei Pharmaceutical Co., Ltd.; and Teijin Pharma Ltd., Grant/research support from: AbbVie Japan GK; Asahi Kasei Corp.; Astellas Pharma Inc.; Ayumi Pharmaceutical Co.; Boehringer Ingelheim Japan, Inc.; Bristol Myers Squibb Co., Ltd., Chugai Pharmaceutical Co., Daiichi-Sankyo, Inc., Eisai Co., Ltd.; Kaken Pharmaceutical Co., Ltd.; Kissei Pharmaceutical Co., Ltd.; Mitsubishi Tanabe Pharma Co.; Nippon Kayaku Co., Ltd.; Sekisui Medical; Taisho Pharmaceutical Co., Ltd.; and Teijin Pharma Ltd.